The use of facsimile machines, modems and other data communication devices is becoming increasingly popular in homes and small businesses. In order to save on costs, this market often transmits data on the same telephone lines as it uses for voice communication. As well, telephone lines may be shared between groups of people or businesses. Although they are not required for outgoing calls, distinctive ringing services provided by telephone companies, operated under trademarks such as Ident-a-call.TM. of Bell Canada, have promoted the sharing of telephone lines in this manner.
Unfortunately, data transmissions are particularly sensitive to a telephone extension going off-hook or on-hook. Often the data transmission will fail. This is not only irritating, but can result in significant expense and delays in re-transmitting the data. This is especially true where an on-line service provider and long distance charges are involved.
A number of devices have been proposed for maintaining privacy in telephone systems. It is possible that they could be used to solve some of the above problems. For example, U.S. Pat. No. 4,809,317 issued to Howe et al on Feb. 28, 1989 for a Telephone Line Exclusion Device describes an exclusion device that interfaces between a single incoming telephone line and two extensions. If a telephone device on one of the two extensions goes off-hook then a relay in the exclusion device locks out the other extension. The Howe device still leaves a number of other problems. For example, the telephone devices that are capable of being excluded are always excluded when the other extension goes off-hook. This means that a call that is meant to be accessed by the excluded device cannot be accessed once another extension is in use. This prevents transferring of calls and conferencing calls between the excluded device and a telephone device on another extension, when the call does not commence on the excluded device.
Also, the exclusion device attaches to the incoming telephone line at the point where it branches into extensions. This means that an ordinary user would not likely be able to install the device. A service call would be required. As well, many modem telephone systems are not installed with extensions emanating from a single point. They are connected from a single cable run through the premises resulting in a ring configuration similar to some computer local area networks. As the Howe device must be connected where two or more extensions are accessible, it would generally be inappropriate for these installations.
Furthermore, the Howe device completely blocks all signals from reaching the excluded telephone device. This would prevent the excluded telephone device from accessing telecommunications features based on frequency shift keyed signals, such as call waiting name or number delivery provided under various trademarks, for example, the CLASS.SM. features of Bellcore.
U.S. Pat. No. 4,218,590 to Rasmussen et al on Aug. 19, 1980 for Key Telephone System having Automatic Exclusion Circuit For Line Privacy discloses a key telephone system passing incoming analog telephone lines through a control unit typically located in the user's home or office. The system redistributes access to the incoming lines to the user stations. A system such as Rasmussen can solve some of the conferencing and transfer issues, however it requires a complex key telephone system and otherwise suffers from the problems of Howe et al.
U.S. Pat. No. 4,805,210 issued to Griffith, Jr. on Feb. 14, 1989 entitled Automatic Telephone Line Sharing And Lockout Apparatus is an automatic lockout device for providing exclusive access to one of the telephone devices attached to the exclusion device. It takes a similar approach to Howe et al and suffers from similar problems.
U.S. Pat. No. 4,987,586 issued to Gross et al on Jan. 22, 1991 entitled Modem-Telephone Interconnect discloses an interface device for connecting a modem and a telephone to a telephone line. It allows either the modem or telephone to be connected to the line, but not both. It is conceptually similar to Howe et al and Griffith, Jr. and suffers from similar problems.
Some telephones have extension-in-use visual indicators. This solves many of the above problems, however a user may still accidentally pick up the phone without noticing the visual indication. Additionally, the visual indicator will typically require a power source, such as a battery or power adaptor. This means that the device could be quite bulky and impractical as a standalone unit.
There are exclusion devices available in the market, (or example Radio Shack fax/atad, Canadian Department of Communications approval number 255 2021A, that connect to an extension line and exclude other extensions, without having to be connected directly to the other extensions and the incoming line as in Howe et al. However these devices continue to prevent transfers and conference call, and block all signals to the excluded extension.
It is an object of the invention to address these or other problems with exclusion devices.